Tesco is facing Britain's largest ever equal pay claim and a possible compensation bill of up to 4 billion pounds (C$7 billion), according to a law firm which has begun legal proceedings. It comes as a campaign for equal pay grows in the U.K.

"It is not clear the names, the salaries and the disbursements above $5,000 in respect of all labour organization employees and contractors need to be publicly disclosed to achieve this more limited objective (of more transparency)," she added.

Opposing MPs called the bill a “bureaucratic monster” and voiced concerns that it could raise costs of union-offered benefit and pension plans.

Terrance Oakey of Merit Canada, a lobby organization for open-shop construction associations, told the Sault Star unions, which enjoy various tax breaks, need to be made more accountable for the benefit of taxpayers and union members.

“The workers forced to make these contributions deserve to know how their money is being spent," he said. "So do members of the general public who subsidize this revenue through the tax system."

The bill is currently being considered before it goes back to the House of Commons for a third reading.

Despite the criticism, Hiebert has backed the bill, saying it is pro-union as it makes union spending transparent and available to members and taxpayers.